Moisture-curable polyolefin pressure-sensitive adhesive

ABSTRACT

A pressure-sensitive adhesive comprises a moisture-curable polymer comprising a polymer prepared by polymerization of at least one α-olefin monomer, said polymer containing hydrolyzable or condensable silyl groups and having a weight average molecular weight of at least 30,000. The pressure-sensitive adhesive can be hot-melt coated without emitting volatiles and then can adhere aggressively to both polar and nonpolar substrates. The PSA has good internal strength at high temperatures.

This is a continuation of application No. 07/585,227 filed Sept. 19,1990, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to pressure-sensitive adhesives that have goodinternal strength at high temperatures. The invention providespressure-sensitive adhesives that can be coated without evolution oforganic matter to provide tapes which are substantially odor-free andphysiologically inert.

2. Description of the Related Art

When considering adhesive tapes, pressure-sensitive adhesive (PSA) tapesare the easiest to use, but for the most part, pressure-sensitiveadhesives do not adhere well to nonpolar substrates. Another shortcomingis that most PSAs are unsuited for uses requiring good internal strengthat elevated temperatures. For example, rubber-resin PSAs tend to softenand degrade when heated. PSAs based on styrene-containing blockcopolymers also do not retain good internal strength when heated,because styrene has a low T_(g) and so softens at moderately elevatedtemperatures. Acrylate PSAs tend to give off toxic vapors at elevatedtemperatures. They typically contain monomeric materials which, even atordinary room temperatures, exude odors that make acrylate PSA tapesgenerally unsuitable for medical uses. Polyisobutylene PSAs are oftenemployed for medical uses because they are physiologically inert, butthey tend to be deficient in internal strength.

PSAs are usually coated from solution or emulsion, thus releasingorganic matter which would pollute the atmosphere unless recovered.Recovery apparatus is expensive and can be dangerous when used torecover inflammable solvents. Hence, it is preferable, when feasible, tohot-melt coat a PSA.

Of known PSAs, silicones best retain high internal strength at elevatedtemperatures, but known silicone PSAs must be coated from organicsolvents. Typically, a metal catalyst is employed to initiate a reactionbetween gum and resin components, especially when good internal strengthat elevated temperatures is required. Most effective are tin catalysts,the toxic nature of which prevents the resulting PSAs from being used inmany important applications such as those involving food or medicalneeds. In spite of such problems and their high price, silicone PSAtapes are used where good internal strength at high temperatures is ofutmost importance, e.g., as electrical insulating tapes and as maskingtapes for use with paints to be baked at high temperatures.

PSAs can be based on α-olefin polymers. For example, U.S. Pat. No.3,635,755 describes PSAs made from homopolymers of C₆ to C₁₁ α-olefinsor from interpolymers of C₂ to C₁₆ α-olefins. These tapes are said toshow substantially no irritation to skin and to have low shear adhesionsthat facilitate non-irritating removal from the human skin.

After noting that prior PSAs based on α-olefin polymers had very poorcohesive (internal) strength, U.S. Pat. No. 3,954,697 discloses thatPSAs provided by copolymers of polypropylene and C₆ to C₁₀ α-olefins canbe hot-melt coated at a melt temperature of at least 350° F. (177° C.)so that the copolymers exhibit no detectable crystallinity by eitherX-ray or DSC techniques. Nothing is said about cohesive strengths atelevated temperatures.

U.S. Pat. No. 4,288,358 discloses that a PSA adhesive based on α-olefinpolymers can be hot-melt coated and can have good resistance to shearadhesion failure, i.e., good internal strength. This is accomplished byblending at least one C₆ to C₁₀ linear α-olefin pol with a plasticizingoil and a tackifying resin. Nothing is said about internal strength atelevated temperatures.

Another publication of PSAs based on α-olefin copolymers wherein themonomers have up to 20 carbon atoms is U.S. Pat. No. 3,542,717.

U.S. Pat. No. 4,178,272 discloses that a hot-melt adhesive whichprovides strong T-peel and lap shear bonds can be made using α-olefinpolymers. The hot-melt adhesive disclosed in this reference is a blendof poly(propyleneco-higher 1-olefin), tackifying resin, and crystallinepolypropylene. The blend is not said to be tacky or provide a PSA. InExample 1, the bonds are made at 200° C.

Another method of producing α-olefin polymers of good internal strengthinvolves grafting silanes onto the polymers as in U.S. Pat. No.4,759,992. The '992 patent relates to applying protective coatings toweatherable substrates such as wood, brick and concrete. The referenceteaches moisture-curable silane-substituted α-olefin polymers that areof low molecular weight as evidenced by a vicosity average molecularweight of between about 500 and about 20,000.

SUMMARY OF THE INVENTION

Briefly, the PSA of the invention provides a moisture-curable polymerwhich is a PSA both before and after being moisture cured and comprisesa polymer prepared by polymerization of at least one α-olefin monomer,the polymer comprising hydrolyzable or condensable silyl groups andhaving a weight average molecular weight of at least 30,000.

The present invention provides a pressuresensitive adhesive which canhave good internal strength at elevated temperatures while avoiding theaforementioned problems. Because of this, the novel PSA can be used formaking automotive masking tapes and other tapes requiring good strengthat elevated temperatures.

Advantages of the novel PSA include

1) the ability to be hot-melt coated without emitting volatiles,

2) being odor-free,

3) being physiologically inert and hence non-allergenic, and

4) the ability to adhere aggressively to both polar and nonpolarsubstrates. Furthermore, large-scale production can produce the novelPSA and PSA tapes at costs comparable to that of any major PSA now onthe market.

In this application:

"alpha-olefin polymer" means a polymer prepared by polymerization of atleast one α-olefin monomer;

"halo" means chloro or bromo,

"Ziegler-Natta (Z-N) catalyst" means a coordination initiator orcatalyst having the properties described by Seymour and Carraher,"Polymer Chemistry", page 296, Mercel Dekker, Inc., N.Y. (1988).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferably, in the PSA of the invention, the novel moisture-curableα-olefin polymer has a hydrocarbyl backbone and the general formula:

    (M.sup.1).sub.x -(M.sup.2).sub.y -(M.sup.3).sub.x          I

wherein

x, y, and z are numbers designating the relative molar amounts of M¹,M², and M³ units that are randomly located in the backbone chain of thepolymer such that the polymer has a weight average molecular weight ofat 30,000, ×is at least 60% of x+y wherein y can be 0, 0.1 to 10% of x+y +z;

M¹ is a repeat unit present in a polymer formed upon polymerization ofan α-olefin having 6 to 14 carbon atoms;

M² is a saturated or unsaturated repeat unit present in a polymer formedupon polymerization of ethylenically-unsaturated hydrocarbons selectedfrom α-olefins having 2 to 20 carbon atoms, non-conjugated dienes having5 to 20 carbon atoms, and non-conjugated mono- andpolyethylenically-unsaturated mono-and polycyclic hydrocarbons having 6to 20 carbon atoms;

M³ is the same as M² but is substituted by a hydrolyzable or condensablesilyl group;

Most preferably, the novel moisture-curable α-olefin polymer has thegeneral formula: ##STR1## wherein

R¹ is an alkyl group having 4 to 12 carbon atoms, preferably 4 to 8carbon atoms, and most preferably about 4 to 6 carbon atoms;

R² is hydrogen or a hydrocarbyl group selected from alkyl groups having1 to 18 carbon atoms and aryl groups having 6 to 12 carbon atoms;

R³ is preferably hydrogen or together with R² and the carbon atoms towhich they are attached is a saturated or unsaturated monocyclic orpolycyclic ring system having 6 to 20 carbon atoms;

x, y, z', and z" are numbers designating the relative molar amounts ofx, y, z', and z" that are randomly located in the backbone chain of thepolymer such that the polymer has a weight average molecular weight ofat least 30,000, x is at least 60% of x +y wherein y can be 0, and z'+z"is 0.1 to 10% of ×+y +z, +z", and z" can be 0; z' and z" =z, in which zis defined above.

R⁴ is a hydrocarbyl group selected from alkyl and alkylene groups having1 to 18 carbon atoms and aryl and arylene groups having 6 to 12 carbonatoms;

R⁵ is hydrogen or together with R⁴ and the carbon atoms to which theyare attached forms a saturated or unsaturated monocyclic or polycyclicring system; the same as disclosed above for R³ ;

R is an alkyl group having 4 to 18 carbon atoms; ##STR2## designates anoptional coordinate bond or the divalent group ##STR3## that joins R_(P)SiX.sub.(3-p) either directly to a carbon atom in R⁴ or to a carbon atomof the ring system formed by R⁴ and R⁵ ;

m is an integer having a value 1 to 6, preferably 3;

R is a hydrocarbyl group selected from alkyl groups having 1 to 18carbon atoms (preferably methyl or ethyl), aryl groups having 6 to 8carbon atoms, and cycloalkyl groups having 5 to 8 carbon atoms;

X is a hydrolyzable or condensable atom or group selected from hydrogen,hydroxy, halogen; hydrocarbyloxy and hydrocarbylcarbonyloxy having 1 to5 carbon atoms, preferably 1 to 3 carbon atoms; and

p is zero, one or two.

Preferably, p is 0 and each X of the hydrolyzable or condensable silylgroup is a hydrocarbyloxy group (more preferably an alkoxy group),because this enhances the moisture-curability of the novel α-olefinpolymer.

In the presence of moisture, the pendant silyl groups, preferablealkoxysilyl groups, of the novel moisture-curable polymer hydrolyze tosilanols that split off water to form a Si-O-Si crosslinked network.

When R¹ contains from 4 to 8 carbon atoms, the novel moisture-curableα-olefin polymer is a tacky PSA at ordinary room temperatures (e.g.,20°-25° C.). When R¹ contains from 9 to 12 carbon atoms, the novelα-olefin polymer is not normally tacky but becomes tacky when heated tomoderately elevated temperatures (e.g., above 25° to 100° C.) andnormally loses that tackiness when cooled to ambient temperature (e.g.,20-25° C.). While tacky, it can form strong bonds under fingertippressure. When R¹ contains from 9 to 12 carbon atoms and R² is an alkylgroup of from 1 to 8 carbon atoms, the novel α-olefin polymer may beslightly tacky at ordinary room temperatures. For some uses, the abilityof a PSA to become tacky only when heated is an important advantage.

The preferred ratio of x plus y groups to z'+z" groups is from 20:1 to200:1 (i.e., 0.5 to 5 mole % z'+z" groups present in the polymer). Asthat ratio increases (percentage of z'+z"groups decreases), the novelα-olefin polymers have increased tackiness, but as that ratio decreases,they have increased internal strength. Hence, that ratio should beselected to afford the desired balance of tackiness and cohesivestrength. For most uses, the best balance is attained when the ratio isbetween 30:1 and 100 1 (i.e., between about 0.3 and 3.2 mole % z, +z"groups present in the polymer). Tackiness can also be increased, or anotherwise non-tacky moisture-curable α-olefin polymer of the inventioncan be made tacky, by blending it with tackifying resin.

Preferably, a moisture-curable α-olefin polymer of the invention has aT_(g) not higher than 0° C., more preferably not higher than -20° C.,and its T"can be as low as -60° or -70° C. A novel PSA α-olefin polymerthat has a low T_(g) tends to have superior adhesion. Furthermore, anα-olefin polymer with a lower T: can be blended with larger amounts oftackifying resin to make coatings that are less shocky.

Preferably, the novel moisture-curable α-olefin polymer has an inherentviscosity (IV) in hexane in the range of 0.5 to 3 dl/g, which valuesroughly correspond to weight average molecular weights of from 50,000 to3,500,000, respectively. Within that preferred range of inherentviscosities, the α-olefin polymer can be hot-melt coated. At an IVsubstantially below that preferred range, the α-olefin polymer would beless likely to attain high internal strength, especially at elevatedtemperatures. At viscosities substantially higher than 3 dl/g, theα-olefin polymer can be coated from solution. At an IV above 5 dl/g, itmay be necessary to employ a solution that is too dilute to becommercially practical.

The novel moisture-curable α-olefin polymer can be produced fromcommercially available starting materials by any of several methods. Afirst method involves the steps of:

a) copolymerizing a C₆ to C₁₄ α-olefin monomer with anω-alkenylhalosilane or ω-alkenylalkoxysilane (wherein the alkenyl grouphas 2 to 20 carbon atoms) using a Z-N (Ziegler-Natta) catalyst toproduce a copolymer containing halosilyl or alkoxysilyl side chains(preferably chlorosilyl side chains), and

b) when the resulting copolymer contains halosilyl side chains, reactingthe copolymer with an alcohol to afford alkoxysilyl side chains.Preferably the alcohol is methanol or ethanol because hydrolysis mayproceed too slowly when using higher alcohols.

The preferred Ziegler-Natta catalysts are complexes of alkylaluminumtogether with a halide of a transition metal from group IV to group VIIIof the Periodic Table in which the alkylaluminum is a compound such astriethylaluminum, tributylaluminum, diethylaluminum chloride, anddibutyl aluminum chloride and the transition metal halide is a compoundsuch as titanium trichloride, titanium tetrachloride, vanadiumtrichloride, vanadium tetrachloride, and vanadium oxytrichloride. Thepreferred catalyst system is diethylaluminum chloride/aluminum activatedtitanium trichloride which is commercially available (Stauffer ChemicalCo.).

Preferably, in the novel α-olefin polymer produced by this first method,M³ has the formula: ##STR4## n is an integer in the range of 3 to 18,preferably to 6, and R, X and p are as defined above.

A second method involves the steps of:

a) copolymerizing a C₆ to C₁₄ α-olefin monomer with a nonconjugatedlinear, mono-, or polycyclic diene using a Z-N catalyst to produce acopolymer containing pendant and/or terminal ethylenic-unsaturation and

b) in the presence of a catalyst, preferably a Pt-containing catalyst,hydrosilating the ethylenic unsaturation with a hydrosilane of theformula

    HSiR.sub.P X(.sub.(3-p)

wherein X, R and p are as defined above. Hydrosilation catalysts, e.g.,organometallics, or rhodium- or platinum-containing catalysts, are wellknown in the art and are commercially available.

In the novel α-olefin polymer produced by this second method, M³ has thesame structure III above when the diene is linear and, when the diene iscyclic, M³ has a structure; such as, for example: ##STR5##

A third method involves the steps of:

a) copolymerizing a C₆ to C₁₄ α-olefin monomer with a nonconjugatedlinear, mono-, or polycyclic diene using Z-N catalyst to produce acopolymer containing pendant and/or terminal ethylenically-unsaturatedchains, and

b) in the presence of an initiator such as peroxide, or by UV radiationin the presence of a photoinitiator, adding a mercaptoalkylalkoxysilane,preferably mercaptopropyltriethoxysilane, to the ethylenic-unsaturationof the side chains.

In the novel α-olefin polymer produced by this third method, M₃ hasstructures such as, ##STR6## wherein R, p, X, and n are as previousinteger in the range of 1 to 6, preferably 3. Because of its sulfurbridge, the resulting α-olefin polymer is not as stable at elevatedtemperatures as is that produced by the second method.

A fourth method involves the steps of

a) polymerizing one or more C₆ to C₁₄ α-olefin monomers alone or with upto 40 mole% of one or more C₂ to C₅ α-olefin monomers or aromaticolefins using a Z-N catalyst to produce a saturated homopolymer orcopolymer,

b) reacting the resulting α-olefin polymer with maleic anhydride in thepresence of a catalyst, preferably a peroxide catalyst and preferably anelectron donor (e.g., triphenyl phosphite or triethyl phosphate) toproduce an adduct, and

c) reacting the maleated α-olefin polymer adduct withaminoalkylalkoxysilane, preferably aminopropyltriethoxysilane, or withisocyanatoalkylalkoxysilane, preferably isocyanatopropyltriethoxysilane,either in solution or in a melt, e.g., in an extruder.

In the novel moisture-curable α-olefin polymer produced by the fourthmethod, M³ has structures such as, for example: ##STR7## wherein R⁶, m,p, R, X, z are as previously defined.

In step b) of the fourth method, when the starting polymer is ahomopolymer, the maleic anhydride attaches to the tertiary carbon byhydrogen abstraction in the presence of an initiator, such as aperoxide, which preferably is dibenzoylperoxide. When the startingpolymer is a copolymer of propylene and a higher α-olefin of from 6 to10 carbon atoms, the maleic anhydride preferentially attaches to thecarbon containing the methyl group. When the starting polymer is acopolymer containing a nonconjugated diene, the maleic anhydridepreferentially goes to the allylic position.

A fifth method involves the steps of:

a) polymerizing a C₆ to C₁₄ α-olefin monomer alone or with up to 40mole% of one or more C, to C° α-olefin monomers using a Z-N catalyst toproduce a saturated homopolymer or a copolymer,

b) reacting maleic anhydride with aminoalkylalkoxysilane or withisocyanatoalkylalkoxysilane (as disclosed previously) to produceimidoalkylalkoxysilane, and

c) reacting the α-olefin polymer produced in step a) with theimidoalkylalkoxysilane in the presence of an initiator such as aperoxide and preferably an electron donor such as a dialkylphosphite,preferably diethylphosphite or dibutylphosphite, either in solution orin melt.

In the novel moisture-curable α-olefin polymer the fifth method, thestructure of M³ is the same as that produced by the fourth method.

Alpha-olefins that can be used in preparing an ethylenically-unsaturatedα-olefin polymer of the invention can have from 2 to 14 carbon atoms.Representative examples include, but are not limited to, ethylene,propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene,1-tetradecene; branched olefins such as 3-methyl-1-butene,3,3-dimethyl-1-butene, 4-methyl-1-pentene, and 3-ethyl-1-pentene; cyclicolefins such as cyclopentene, cyclohexene, 3-methylcyclopentene,4-n-butylcyclohexene, bicyclo[2.2.1]hept-2-ene,1,7,7-trimethylbicyclo[2.2.1]hept-2-ene (bornylene)bicyclo[3.2.0]hept-2-ene,bicyclo[3.2.0]hept-6-ene,bicyclo[2.2.0]oct-2-ene, andtricyclo[3.2.2]non-6-ene; and aromatic olefins such as allylbenzene,lH-indene, 3-methyl-lH-indene, and styrene.

Non-conjugated dienes that can be used in the α-olefin polymer of theinvention have 5 to 14 carbon atoms. Representative examples include,but are not limited to, 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene,1,7-octadiene, 1,13-tetradecadiene, 1,19-eicosadiene, and the like;cyclic dienes such as 1,4-cyclohexadiene, bicyclo[2.2.1]hept-2,5-diene,bicyclo[2.2.2]oct-2,5-diene, 4-vinylcyclohex-1-ene,bicyclo[2.2.2]oct-2,6-diene,1,7,7-trimethylbicyclo[2.2.1]hept-2,5-diene, dicyclopentadiene,5-allylbicyclo[2.2.1]hept-2-ene, 1,5-cyclooctadiene; and aromatic dienessuch as 1,4-diallylbenzene, 4-allyl-1H-indene and the like.

Moisture-curable α-olefin polymers produced by each of the fiveforegoing methods can be hot-melt coated onto flexible backings withoutevolution of volatile matter to produce PSA tapes of the invention. ThePSA coatings of the resulting tapes can be hydrolyzed to form a Si-O-Sicrosslinked network simply upon being exposed to the moisture of theatmosphere. Faster crosslinking is achieved in the presence of a silanolcondensation catalyst. Suitable catalysts include organic metalcompounds such as tin carboxylates and titanium esters or chelates,e.g., tetrabutyltitanate and bis(acetylacetonyl)di-isopropyl titanate;organic bases such as ethylamine, hexylamine and piperidine; and acidssuch as the mineral acids and fatty acids. The preferred catalysts arethe organic tin compounds, for example, dibutyltindilaurate,dibutyltindiacetate and dibutyltindioctoate. Typically, such catalystsare added in amounts between one part to about 3 parts by weight per 100parts by weight of the moisture-curable α-olefin polymer.

In the absence of a silanol condensation catalyst, hydrolysis proceedsslowly at low relative humidity (less than 50% relative humidity), sothat it may be desirable to subject the coated tapes to conditions ofhigh relative humidity (at least 50%) and moderately elevatedtemperature (e.g., 30° to 100° C.), preferably immediately following thecoating step. Instead, the coating can be caused to pick up moisture(e.g., by being exposed to steam), and the moisture-bearing tape can bewound up into a jumbo roll, wherein the support can have a releasecoating on its backside, which is then heated in an oven until the PSAcoating has become moisture-cured. Another technique involves blending anovel α-olefin polymer with one to ten weight percent, preferably one totwo weight percent of a hydrated salt prior to coating and later heatingthe tape to produce the moisture-curing, either while the tape is inroll form or after it has been put to use. Suitable hydrated saltsinclude CaSO' 5H₂ O, MgSO₄.7H₂ O, BaSO₄ 2H₂ O, (CH₃ COO)₂ Ba. 2H₂ O,BaCl₂. 2H₂ O, CaSO₄.2H₂ O, Na₂ B₄ O; 10H₂ O, AlNH₃ (SO₄)₂. 12H₂ O,Al(OH)₃. XH ₂ O, Al(NO₃)₃.9H₂ O, and Al₂ (SO₄)₃ 16H₂ O.

A blend of the novel α-olefin polymer with a tackifying resin can havelower viscosity and thus be more readily hot-melt coated, and theresulting coatings can have greater tackiness and peel adhesion ascompared to coatings of the novel α-olefin polymer alone. The inclusionof tackifying resin also tends to enhance internal strength. Usefultackifying resins include resins derived by polymerization of C₅ to C₉unsaturated hydrocarbon monomers, polyterpenes, synthetic polyterpenesand the like. Hydrocarbon tackifying resins can be prepared bypolymerization of monomers consisting primarily of olefins and diolefinsand include, for example, residual by-product monomers of the isoprenemanufacturing process. These hydrocarbon tackifying resins typicallyexhibit Ball and Ring softening points from about 80° C. to about 145°C.; acid numbers from about 0 to 2, and saponification values of lessthan one. Examples of such commercially available resins based on a C₅olefin fraction of this type are Wingtack™ 95 and Wingtack™115tackifying resins available from Goodyear Tire and Rubber Co. Otherhydrocarbon resins include Regalrez™ 1078 and Regalrez™ 1126 availablefrom Hercules Chemical Co., Inc., Escorex™ resins available from ExxonChemical Co., and Arkon™P115 available from Arakawa Chemical Co.

The tackifying resin may contain ethylenic unsaturation. However,saturated tackifying resins are preferred for those applications whereoxidation resistance is important. The total amount of tackifying resinin the PSA of the invention preferably is from 0 to 150 parts, morepreferably 5 to 50 parts and most preferably 25 to 35 parts by weightper 100 parts of moisture-curable α-olefin polymer.

The use of diluent in the novel PSA is desirable from the standpoint ofprocessing. Illustrative of the inert diluents which may be employed arevegetable oils, mineral oils such as napthenic and paraffinicdistillates, and esters such as dibutyl phthalate, dioctyl phthlate,dioctyl adipate. Between 0 and about 300 parts by weight of diluent,based on 100 parts by weight of the novel silyl-substituted α-olefinpolymer, can be employed.

The PSA of this invention is typically prepared by blending componentsin any order employing conventional mixing apparatus. In order to avoidpremature cure of the blends, they should be stored either undernitrogen or under low humidity conditions.

The PSA of the present invention forms strong bonds to a wide variety ofmaterials such as plastic films, glass, and monomolecular oxide layersof metal substrates such as steel and aluminum. Extremely thin coatings(e.g., on the order of 0.1 to 10 μm) of the novel PSA can function aspolymeric coupling agents. For example, glass beads or microbubbles thatare to be used as a filler for a resinous body can be provided withultrathin coatings of the novel PSA to enhance the integrity of thatbody. In doing so, the Si-O-Si crosslinked network includes Si atoms ofthe glass, while the nonpolar moiety of the novel PSA bonds to theresinous body. Because of this dual functionability of the novel PSA, acellulose or concrete substrate that is filled with plastic particlessuch as plastic bubbles can have enhanced integrity when the plasticparticles have ultrathin coatings of the novel PSA. Other fillerparticles which can adhere more strongly to a matrix when treated withultrathin coatings of the novel PSA include fumed silica and metaloxides such as zirconia, alumina, and titanium dioxide.

The novel PSA can be used in combination with conventional polar PSAs toafford exceedingly strong bonds between plastics and metals. For suchuses, an acrylate PSA can be coated onto a release liner, and a layer ofthe novel PSA can be hot-melt coated onto the acrylate coating. Theexposed face of the resulting double-coated transfer tape can be adheredto a plastic body side molding. Then after stripping off the liner, theacrylate PSA coating can bond the body side molding to a paintedautomobile. The same results can be achieved by applying layers of thenovel PSA and acrylate PSA to opposite sides of a flexible carrier film,e.g., fiberglass, ceramic, metal, or polymeric, which becomes part ofthe final assembly.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the materials and amounts thereof recited inthese as well as other conditions and details, should not be construedto unduly limit this invention.

EXAMPLES TEST METHODS

The test procedures used in the examples to evaluate and compare theproperties of the PSA compositions and tapes made from them are industrystandard tests. These tests are described in detail in variouspublications of the American Society for Testing Materials (ASTM),Phila., PA and the Pressure Sensitive Tape Council (PSTC), Glenview IL.References to these standards are also given.

Shear Strength (ASTM D-3654-78; PSTC - 7)

Shear strength is a measure of the cohesiveness or internal strength ofan adhesive. It is based upon the amount of force required to pull anadhesive strip from a standard flat surface in a direction parallel tothe surface to which it has been affixed with a definite pressure. It ismeasured in units of time (minutes) required to pull a standard area ofPSA coated sheet material from a stainless steel test panel under stressof a constant, standard load.

The tests are conducted on adhesive coated strips applied to a stainlesssteel panel such that a 12.7 mm by 12.7 mm portion of each strip is infirm contact with the panel with one end portion of the tape being free.The panel with coated strip attached is held in a rack such that theexposed face of the backing of the strip forms an angle of 182° at theedge of the panel when a mass is applied as a hanging weight from thefree end of the coated strip. The 2° greater than 180° is used to negatepeel forces, thus ensuring that only the shear forces are measured todetermine the holding power of the tape being tested. The time elapsedfor each test specimen to separate from the steel panel is recorded asthe shear strength.

The time at which the mass falls (average of two specimens) is called"Shear at RT" (when measured at room temperature) or "Shear at 70° C."(when measured at 70° C). When reported as "1000+", the tape had notfailed after 1000 minutes. The mode of failure is indicated as follows:

pp= Pop-off, i.e., 75-100% adhesive failure from steel plate

sp= Adhesive split leaving >25% residue

The pop-off failure mode is indicative of adhesive failure of theadhesive/steel interfacial bond as opposed to cohesive failure of theadhesive.

Peel Value [ASTM D 3330-78; PSTC - 1 (11/75)]

The peel adhesion is the force required to remove a PSA coated testspecimen from a test panel measured at a specific angle and rate ofremoval. In the examples, this force is expressed in Newtons perdecimeter width (N/dm) of coated sheet. The procedure followed is:

1) A test specimen 12.7 mm wide is applied to a horizontally positionedclean glass test plate. A 2.2 kg rubber roller is used to press a 12.7cm length of specimen into firm contact with the glass surface.

2) The free end of the specimen is doubled back nearly touching itselfso the angle of removal is 180° . The free end is attached to theadhesion tester scale.

3) The glass test plate is clamped in the jaws of tensile testingmachine which moves the plate away from the scale at a constant rate of2.3 meters per minute.

4) The scale reading in Newtons ("Peel Value") is recorded as the tapeis peeled from the glass surface.

Removal Test

Used in this test is an aluminum panel, the test surface of which has apaint to which masking tapes are adhered with difficulty, e.g., thepaint is an automotive basecoat/clearcoat (BC/CC) acrylic enamel paintsystem or the automotive 50J.sup.™ acrylic enamel point of Ford MotorCo.

Tapes are adhered at room temperature by their adhesives to the testsurface, followed by two passes of a 4.5-pound (2-kg) rubber-coatedmetal roller. After one hour in an air-circulating oven at either 121°C. or 150° C., the tape is peeled back while hot at an angle of 45° atan approximate rate of 1.9 m/min. across half of the panel. Aftercooling to room temperature, the tape is peeled from the other half ofthe panel. The panel is examined visually for any adhesive residue.([Polymers 1-3 illustrate the above-outlined "first method" of making amoisture-curable α-olefin polymer of the invention; Polymers 4-9, the"second method"; Polymers 10-11, the "third method"; and Polymers 12-15,the "fourth method".

Polymer No. 1: Synthesis of Poly(1-hexene-co-triethoxyoct-7-enylsilane)(99.5:0.5 mol ratio)

The following reactants were charged in the order named to a dry,argon-filled, circulating-water-jacketed glass reactor equipped withstirrer and dry ice condenser: 100 g of toluene, 20 g of 1-hexene(Gulftene-6.sup.™ available from Gulf Oil) which had been passed throughalumina/silica to remove impurities and then dried over molecularsieves), 0.27 g of triethoxyoct-7-enylsilane and 0.0194 g of activatedaluminum titanium trichloride (AATiCl₃.sup.™ catalyst from StaufferChemical Co.) (1.26 10⁻³ mole). Copolymerization was initiated by theslow addition of 1.1 ml (1.96×10⁻³ mole) of diethylaluminum chloride of1.8 M in toluene. Within 5 minutes the polymer became insoluble andhence unusable, probably due to hydrolysis of alkoxysilane groups in thepresence of Lewis acid catalyst.

The gellation could have been avoided by replacing the ethoxysilane witha higher alkoxysilane such as an isopropoxysilane or a t-butoxysilane.Even then, the hydrolysis and crosslinking would proceed slowly.

Polymer No. 2: Synthesis ofPoly(l-hexene-co-dimethylchloroct-7-enylsilane) (99.5:0.5 mole ratio)

The reaction was carried out in the same way as in Example 1 exceptusing 20 g of 1-octene and 0.21 g of dimethylchloroct-7-enylsilane intoluene in the presence of diethylaluminum chloride and "AATiCl₃ "catalyst in 1:1 molar ratio. After polymerization, the reactants wereprecipitated in methanol to convert the chlorosilane to thecorresponding methoxysilane.

Polymer No. 3: Synthesis ofPoly(1-hexene-co-[bicyclo(2.2.1)hept-5-en-2-yl]methyldichlorosilane)(99.5/0.5 mole ratio)

The reaction was carried out in the same manner as in Example 1 exceptusing 20 g of 1-octene and 0.3 g of[bicyclo(2.2.1)hept-5-en-2-yl]methyldichlorosilane in toluene in thepresence of diethylaluminum chloride and "AATiCl₃ " catalyst in 1:1molar ratio. After polymerization the reactants were precipitated inmethanol to convert the chlorosilane to the corresponding methoxysilane.

Polymer No. 4:

50 g of 1-hexene-co-1,7-octadiene copolymer (97:3 mole ratio) wasprepared using the procedure for Polymer No. 1 except using1,7-octadiene instead of the silane having an inherent viscosity inheptane of 1.9 dl/gm was dissolved in 500 g of toluene. This wasrefluxed under nitrogen, and about 20 ml of toluene was distilled out toensure the removal of the water in the system. 2.9 g of triethoxysilaneand 100 ppm of bis(divinyltetramethyldisiloxane)platinum(0) catalystwere added. The reaction was run for 48 hours. Progress of the reactionwas monitored by spectral analysis. At the end of the reaction, thecopolymer was precipitated in dry methanol under anhydrous conditions.The silyl moiety of the copolymer was found by spectral analysis to be2.7 mole%.

Polymer No. 5:

Polymer No. 4 was repeated except using 1.45 g of the triethoxysilane.The reaction was refluxed for 40 hours for completion of the reaction.The silyl moiety of the copolymer was found by spectral analysis to be1.2 mole%.

Polymer No. 6:

Polymer No. 4 was repeated except using 0.73 g of the triethoxysilane.The reaction was refluxed for 40 hours for completion of the reaction.The silyl moiety of the copolymer was found by spectral analysis to be0.63 mole%.

Polymer No. 7:

Polymer No. 4 was repeated except using 2.4 g of thediethoxymethylsilane. The reaction was refluxed for 72 hours forcompletion of the reaction. The silyl moiety of the copolymer was foundby spectral analysis to be 1.2 mole%.

Polymer No. 8:

50 g of 1-octene-co-1,7-octadiene (97:3 mole ratio) copolymer wasprepared using the procedure of Polymer No. 4 except that 1-octene wasused instead of 1-hexene and had an inherent viscosity in heptane of 2.1dl/gm and was dissolved in 500 g of toluene. This was refluxed undernitrogen, and about 20 ml of toluene was distilled out to ensurecomplete removal of water in the system. 2.2 g of triethoxysilane and100 ppm of the same catalyst as used in Polymer No. 4 were added. Thereaction was run for 72 hours. Progress of the reaction was checked byspectral analysis. The silyl moiety of the copolymer was found byspectral analysis to be 2.8 mole%.

Polymer No. 9:

50 g of octene-co-1,7-octadiene (97:3 mole ratio) copolymer, prepared asdescribed above, with an inherent viscosity in heptane of 2.1 dl/gm wasdissolved in toluene. The solution was flushed with nitrogen for an hourfollowed by distillation of 20 ml of toluene to ensure no moisturepresent in the system. 2.0 g of benzoyl peroxide and 2.2 g oftriethoxysilane were added, and the mixture was refluxed for 72 hours.The progress of the reaction was checked by spectral analysis. The silylmoiety of the copolymer was found by spectral analysis to be 1.4 mole%.

Polymer No. 10:

30 g of hexene-co-1,7-octadiene (97:3) copolymer, prepared as describedabove, with an inherent viscosity in heptane of 1.9 dl/gm was dissolvedin toluene. The solution was flushed with nitrogen for an hour followedby distillation of 20 ml of toluene to ensure no moisture present in thesystem. 2.08 g of mercaptopropyltrimethoxysilane and 1.5 g ofazobisisobutyronitrile were added, and the mixture was refluxed for 18hours. The progress of the reaction was checked by spectral analysis.The silyl moiety of the copolymer was found by spectral analysis to be1.9 mole%.

Polymer No. 11:

30 g of hexene-co-1,7-octadiene (97:3) copolymer, prepared as describedabove, with an inherent viscosity in heptane of 1.9 dl/gm was dissolvedin toluene. The solution was flushed with nitrogen for an hour followedby distillation of 20 ml of toluene to ensure no moisture present in thesystem. 1.04 g of mercaptopropyltriethoxysilane and 0.6 g ofbenzophenone photoinitiator were added, and the mixture wasphotoirradiated for 15 hours. The polymer underwent gellation during thereaction.

Polymer No. 12:

Hexene-co-propylene (60:40 mole ratio) copolmer, prepared as describedabove, was adducted with 3.8 mole% of maleic anhydride 50 g of thisadduct, which had a melt viscosity of 9840 cp at 190° C., was dissolvedin 150 g of toluene. This was refluxed for two hours in inertatmosphere, and a small portion of toluene was distilled to remove anywater in the system. The mixture was reacted with 1 g ofaminopropyltriethoxysilane at room temperature for 3 hours followed byrefluxing for another two hours to ensure the completion of thereaction.

Polymer No. 13:

50 g of the adduct of Polymer No. 12 was dissolved in 150 g of toluene.This was refluxed under nitrogen for two hours, and a small portion oftoluene was distilled to remove any water in the system. 1 g ofisocyanatopropyltriethoxysilane was added to the solution. The contentswere heated at 60°-65° C. for about three hours for the reaction tocomplete.

Polymer No. 14

The procedure for making Polymer No. 12 was repeated except that thehexene-propylene copolymer was converted to an adduct with 1.2 mole% ofmaleic anhydride (melt viscosity of 7680 cp at 190° C).

Polymer No. 15

50 g of the adduct of Polymer No. 12 was dissolved in 150 g of toluene.This was refluxed for three hours under nitrogen, and a small portion oftoluene was distilled to remove any water in the system. The mixture wasreacted with 3 g of aminopropyltriethoxysilane at room temperature forthree hours followed by refluxing for another two hours to ensure thecompletion of the reaction.

    ______________________________________                                        Comparative Polymer Nos. C-1 through C-4                                      (prepared as described above)                                                 ______________________________________                                        C-1   Copolymer of hexene-co-1,7-octadiene (97:3 mole ratio)                  C-2   Copolymer of octene-co-1,7-octadiene (97:3 mole ratio)                  C-3   Copolymer of hexene-co-propylene (60:40 mole ratio)                           adducted with 3.8 mole % maleic anhydride                               C-4   Copolymer of hexene-co-propylene (60:40 mole ratio)                           adducted with 1.2 mole % maleic anhydride                               ______________________________________                                    

EXAMPLES 1-38 Preparation of Pressure-Sensitive Adhesive

Each of Polymers No. 3-15 and of Comparative Polymers No. C-1 to C-4 wasformulated into a pressure-sensitive adhesive by solution blending intoluene: the copolymer, 25 phr (parts per hundred parts of polymer) of asynthetic hydrocarbon tackifier resin, and 1.0 phr stabilizer (Irganox™1010) Each blend was knife coated at a thickness of 25 μm onto 38-μmbiaxially oriented poly(ethyleneterephthlate) film. The coating wasdried for 5 minutes at 150° F. (65° C.) and conditioned for 24 hours at90% humidity. Some of the adhesive compositions were also made adding 1%of dibutyltin dilaurate catalyst in order to examine the efficacy ofhydrolysis of alkoxysilyl groups under the humid conditions.

Tackifiers used in the PSA formulations were:

A Wingtack 115™

B Regalrez™ 1126

C Arkon™ P115

Tape testing was carried out according to the test methods previouslydescribed, and the results are detailed in Tables I, II and III.

                  TABLE I                                                         ______________________________________                                        PSA Properties of PSA Tapes Made from Polymers                                3-15 and Comparative Polymers                                                                              Peel   Shear at RT                               Ex-   Polymer  Tin           Value  (1 Kg)                                    ample No.      Cat.   Tackifier                                                                            (N/dm) (Min.) MOF*                               ______________________________________                                         1     3       --     --     24       30   sp                                  2     3       1      --     20       52   pp                                  3     3       1      A      65       340  sp                                  4     4       --     --     18       19   pp                                  5     4       1      --     16       55   pp                                  6     4       1      A      62       185  pp                                  7     4       1      B      65     1,239  sp                                  8     4       1      C      58     1,540  sp                                  9     6       --     --     23       24   pp                                 10     6       1      --     20       99   pp                                 11     6       1      A      59       145  pp                                 12     6       1      B      62       542  sp                                 13     8       --     --     19       10   sp                                 14     8       1      --     13       54   pp                                 15     8       1      A      49       134  pp                                 16     8       1      B      53       234  pp                                 17     8       1      C      51       138  pp                                 18    10       1      --     19       102  pp                                 19    10       1      A      64      1,000+                                   20    10       1      B      58     2,534                                     21    10       1      C      62     1,345                                     22    13       --     --     59       93   pp                                 23    13       1      --     53       247  pp                                 24    13       --     B      97     1,357  sp                                 25    13       1      B      72     9,420                                     26    15       --     --     59       206  pp                                 27    15       1      --     57     2,678  pp                                 28    15       --     B      88       994                                     29    15       1      B      66     1,771                                     30    C-1                    29        5   sp                                 31    C-2                    16        1   sp                                 32    C-3                    71       85   sp                                 33    C-4                    63       65   sp                                 ______________________________________                                         *MOF = Mode of Failure                                                        sp = split(cohesive); pp = popoff(adhesive)                              

The data in TABLE I show significant improvements in PSA properties canbe achieved when using Polymers 2-12, and 14-29 as compared toComparative Polymers C-1 to C-4. Where MOF failure was split (cohesive)and shear values were less than 100, the value of a polymer as a PSA waslow. Upon crosslinking, the MOF changed to pop-off (adhesive failure)which is evidence of significant improvement in internal strength.

                  TABLE II                                                        ______________________________________                                        Shear Properties of PSA Tapes at Elevated Temperatures                                          Shear at 70° C. (min.)                               Example                                                                              Polymer No.                                                                              Tackifier 200 g 500 g 1000 g                                ______________________________________                                        34     4          C         235    74    10                                   35     6          B         175    68    9                                    36     8          B         583   246   103                                   37     C-1        C          5    <1    <1                                    38     C-3        B          10    5    <1                                    ______________________________________                                    

The data in TABLE II show improved shear strength at elevatedtemperature for polymers of the invention comprising tackifier comparedto comparative samples with tackifier.

                  TABLE III                                                       ______________________________________                                        Removal Test                                                                  Residue left on BC/CC                                                                             Residue left on 50J                                       Panel after 60 min. at                                                                            Panel after 60 min. at                                    Example                                                                              121° C.                                                                           150° C.                                                                          121° C.                                                                         150° C.                           ______________________________________                                         4      5%         5%        10%      25%                                      5     0          0         0        0                                         6     0           2%       0        0                                         7     0           5%       0         10%                                      8     0          0         0         2%                                      12      10%        50%       25%     100%                                     13     0           2%       0         5%                                      14     0          0         0        0                                        15     0          0         0        0                                        16     0           5%        2%       10%                                     17     0          0         0        0                                        18      10%        50%       25%     100%                                     19      10%        25%       10%      75%                                     20      5%         50%       10%      75%                                     21      5%         15%       10%      25%                                     22     100%       100%      100%     100%                                     23      75%        75%      100%     100%                                     26      15%        25%       25%      75%                                     27     0           5%       0         2%                                      29     0          0         0        0                                        30     100%       100%       75%     100%                                     31      75%        90%       75%     100%                                     32     100%       100%      100%     100%                                     33     100%       100%       75%     100%                                     ______________________________________                                    

The data in TABLE III show that crosslinked polymers performed betterthan non-crosslinked polymers in the experimental removal test. Up to 10percent residue is considered acceptable.

A tin catalyst was not employed with Comparative Polymers C-1 to C-4,because it would not have had any beneficial effect in the absence ofalkoxysilyl groups.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

What is claimed is:
 1. A pressure-sensitive adhesive comprising a tackymoisture-curable copolymer comprising a polymeric α-olefin backbone andhaving the general formula:

    (M.sup.1).sub.x -(M.sup.2).sub.y -(M.sup.3) .sub.z

wherein x, y, and z are numbers designating the relative molar amountsof M¹, M², and M³ units that are randomly located in the backbone chainof the polymer such that the polymer has a weight average molecularweight of at least 30,000, x is at least 60% of x+y, and z is 0.1 to 10%of x+y+z; M¹ is a divalent unit present in a polymer formed onpolymerization of an α-olefin having 6 to 14 carbon atoms; M² is asaturated or unsaturated divalent unit present in a polymer formed bypolymerization of an ethylenically-unsaturated hydrocarbon selected fromα-olefins having 2 to 14 carbon atoms, non-conjungated dienes having 5to 20 carbon atoms, and non-conjugated mono- andpolyehtylenically-unsaturated mono-and polycyclic hydrocarbons having 6to 20 carbon atoms; M³ is the same as M² but is substituted by ahydrolyzable or condensation silyl group; said copolymer when curedbeing tacky and having a weight average molecular weight of at least50,000.
 2. The pressure-sensitive adhesive as defined in claim 1 whereinsaid silyl groups of said moisture-curable α-olefin polymer have beenhydrolyzed to form a Si-O-Si crosslinked network.
 3. Thepressure-sensitive adhesive as defined in claim 1 wherein saidmoisture-curable α-olefin polymer has a T_(g) not higher than -20 C. 4.The pressure-sensitive adhesive as defined in claim 1 wherein saidmoisture-curable α-olefin polymer has an inherent viscosity in toluenein the range of 0.5 to 5 dl/g.
 5. A pressure-sensitive adhesivecomprising a moisture-curable copolymer comprising a polymeric α-olefinbackbone and having the general formula ##STR8## wherein R¹ is an alkylgroup having 4 to 12 carbon atoms;R² is a hydrogen or a hydrocarbylgroup selected from alkyl groups having 1 to 18 carbon atoms and arylgroups having 6 to 12 carbon atoms; R³ is hydrogen or R³ together withR² and the carbon atoms to which they are attached is a saturated orunsaturated, monocyclic or polycyclic ring system having 6 to 20 carbonatoms; x, y, z', and z" are numbers designating the relative molaramounts of x, y, z', and z" that are randomly located in the backbonechain of the polymer such that the polymer has a weight averagemolecular weight of at least 30,000, x is at least 60% of x+y wherein ycan be zero, (z'+z") is 0.1 to 10% of x+y+z'+z" and z" can be 0, andz'+z"=z which is defined in claim 2; R⁴ is a hydrocarbyl group selectedfrom alkyl and alkylene groups having 1 to 18 carbon atoms and aryl andarylene groups having 6 to 12 carbon atoms; R⁵ is hydrogen or togetherwith R⁴ and the carbon atoms to whcih they are attached forms asaturated or unsaturated monocyclic or polycyclic ring system having 6to 20 carbon atoms; R⁶ is an alkyl group having 4 to 18 carbon atoms;##STR9## designates a coordinate bond or the divalent group ##STR10##that joins R_(p) SiX.sub.(3-p)) either directly to a carbon atom in R⁴to a carbon atom of the ring system formed by R⁴ and R⁵ ; m is aninteger having a value 1 to 6; R is a hydrocarbyl group selected fromalkyl groups having 1 to 18 carbon atoms, aryl groups having 6 to 8carbon atoms, and cycloalkyl groups having 5 to 8 carbon atoms; X is ahydrolyzable or condensable atom or group selected from hydrogen,hydroxy, hydrocarbyloxy, hydrocarbonyloxy, and halogen; and p is zero,one or two.
 6. The pressure-sensitive adhesive as defined in claim 1wherein M³ comprises from 6 to 10 carbon atoms and said α-olefin polymeris tacky at 20° to 25° C.
 7. The pressure-sensitive adhesive as definedin claim 1 wherein M¹ comprises from 11 to 14 carbon atoms, and saidα-olefin polymer is tacky when heated to a temperature in the rangeabove 25° to 100° C. and loses that tackiness when cooled to 20° to 25°C.
 8. A pressure-sensitive adhesive as defined in claim 1 wherein theratio of x and y groups to z groups of the moisture-curable α-olefinpolymer is from 30:1 to 100:1.
 9. A pressure-sensitive adhesive asdefined in claim 6 wherein p is 0-6 and each X is an hydrocarbyloxygroup.
 10. The pressure-sensitive adhesive according to claim 1 whereiny in said formula equals zero.
 11. The pressure-sensitive adhesive asdefined in claim 5 wherein said silyl groups of said moisture-curableα-olefin polymer have been hydrolyzed to form a Si-O-Si crosslinkednetwork.
 12. The pressure-sensitive adhesive as defined in claim 5wherein said moisture-curable α-olefin polymer has a T_(g) not higherthan -20° C.
 13. The pressure-sensitive adhesive as defined in claim 5wherein said moisture-curable α-olefin polymer has an inherent viscosityin toluene in the range of 0.5 to 5 dl/g.
 14. A pressure-sensitiveadhesive as defined in claim 5 wherein the ratio of x and y groups to(z'+z") groups of the moisture-curable α- olefin polymer is from 30:1 to100:1.